Implicit multiplication with parens: improve error message

[sharkdp]

This happens frequently. Someone tries to use implicit multiplication with a factor in parens. This doesn't work and is parsed as a function call pi(…).

>>> 2 pi (3 / 4)
error: Could not solve the following constraints:
  Scalar ~ Fn[(Scalar) -> T288
.. while trying to infer types in the (elaborated) statement:
  2 × pi(3 / 4)
]
 = Consider adding type annotations to get more precise error messages.

We should not show a constraint-solver error message in this case but rather catch it directly and show a good error message.